Ultra violet light curable inks, referred to herein as UV ink, are frequently used in printing because they can provide a number of advantages, such as high opacity, water resistance, flexibility, chemical resistivity and good adhesion to non-porous substrates. A UV ink can be applied to a substrate in a solution form and then irradiated with UV light in order to cure the ink into a solid form. Some types of UV ink are solutions that include monomers, oligomers and a photoinitiator, which in combination with the UV radiation, cures the ink. The photoinitiator can absorb UV energy and break into reactive materials that then polymerize or crosslink components in the UV ink. Both free radicals and cationic type photoinitiators are used in UV inks, with the free radical type being more common. Free radical photoinitiator reactions do not continue after the UV energy source is removed.
UV inks can be applied to the desired substrate by using a number of printing processes, such as a screen printing process or ink jet printing process. Ink jet printers typically can be categorized as continuous flow type printers or drop on demand type printers. Ink jet printers also can either have printheads with a limited number of nozzles and that scan the width of the substrate during printing or that are fixed, such as in a page width printing device. Drop on demand type printers that have page width print heads or print bars have multiple nozzles, with some nozzles being fired less frequently than other nozzles during printing.